An adaptor plate assembly for use in interfacing a transmission gear housing having a standard bolt/hole pattern with a power takeoff unit having a non-standard bolt/hole pattern is disclosed. An adaptor plate is positioned between the gear housing and the power takeoff unit. The adaptor plate has passageways in alignment with standard apertures in the gear housing and with openings in the power takeoff unit. Guide and support fasteners having guide heads are initially positioned in ones of the passageways of the adaptor plate and in the housing apertures. The power takeoff unit is initially guided and supported by the guide heads. Securement fasteners are then used to complete the connection of the power takeoff unit to the adaptor plate and the gear housing.